The present invention relates to a solenoid valve and more particularly to a solenoid valve to be used, for example, for controlling the pressure of a diaphragm chamber in a diaphragm type flow control valve.
In internal combustion engines, diaphragm type flow control valves have been used for adjusting the intake volume or for adjusting the amount of exhaust gas to be recycled in EGR (Exhaust Gas Recirculation). Solenoid valves which have heretofore been used for controlling the pressure of a diaphragm chamber are of a structure in which a valve member adapted to close a fluid flowing port by virtue of a spring force is moved in its opening direction by an electromagnetic force. In this type of pressure control, for example, the diaphragm chamber is connected directly to the atmosphere side and connected also to a negative pressure source such as an intake manifold or the like through a solenoid valve, and its internal pressure is controlled to a predetermined level by opening and closing the solenoid valve at a constant period. The open/close cycle of the solenoid valve usually reaches about 20 Hz and thus the condition of use is fairly severer than in other uses of the valve. Consequently, the solenoid valve of such conventional structure as referred to above involves the problem that its service life is shortened by the fatigure of a spring, the wear of a valve stopper which functions to restrict the range of movement of the valve member, etc.